Apparatus for filtering and coalescing liquids

ABSTRACT

An apparatus for removing contaminants from a liquid comprises a casing and a tubular filter dividing the casing into two compartments. The tubular filter is formed of fibers attached at each end to end supports which are movable axially relative to one another and rotable relative to one another about the longitudinal axis of the filter. A helical spring is disposed within the tubular filter and is so dimensioned that it does not close when the end supports are in their closest operational position. The spring resists inward movement of the fibers when the end supports are moved axially towards each other and rotated to twist the fiber, thereby preventing the compartment defined by the interior of the tubular filter from tending to close.

This application is a continuation of application Ser. No. 07/671,784filed Mar. 21, 1991, now abandoned, which is based on InternationalApplication PCT/GB89/01115, filed Sep. 21, 1989, which in turn is basedon British Application 8822249.2, filed Sep. 22, 1988. Priority based onall such earlier application is claimed.

The present invention relates to apparatus for filtering solids fromliquids or for coalescing droplets of one liquid dispersed in anotherliquid.

EP 0 004 724 discloses an apparatus for removing contaminants from aliquid which comprises bundles of fibres aligned parallel to one anotherbetween two end plates. The end plates may be moved axially to stretchor compress the fibres. Liquid flows through the apparatus parallel tothe fibre bundles.

EP 0 207 797 discloses another apparatus for removing contaminants froma liquid. This apparatus also comprises fibres connected at each end toend supports, which end supports can be moved away from or towards eachother to place the fibres under tension or to relax any applied tension.The end supports can also be rotated relative to each other. The fibresare attached to the end supports so as to form a tube of fibressurrounding a central tubular core provided with perforations. Thefibres are in turn surrounded by a perforated tube which restrains thefibres from radial movement (in relation to the axis of the tubularcore). The liquid to be treated passes across the fibres between thecentral core and an outer compartment surrounding the fibres. In use theend supports are moved towards one another and rotated relative to oneanother to twist the fibres and to compress them against the perforatedtube.

An arrangement of perforated inner and outer tubes with fibres arrangedparallel to the axis of the tubes is disclosed in U.S. Pat. No. 4 299699.

The disadvantage of using perforated inner tubes is that they impose arestriction on the flow through the apparatus so giving increasedpressure drop if the rate of flow is to be sustained. Because liquid canonly pass through relatively narrow openings the local liquid velocitynear these openings will be relatively high which may disturb particlesof contaminants already deposited on the fibres. The techniques requiredto produce perforated tubes will also increase the cost of theapparatus. In the case of apparatus which requires both axial as well asrotary movement of the end supports it will be necessary to providelengths of perforated tube in excess of the length required to givesupport to the fibre bundle in the shortened operational position inorder to be able to support the fibres in the elongated positionrequired for back-washing. This will increase the mechanical complexityof the apparatus. The production of perforated tube is a relativelyexpensive process. It would be desirable to provide an apparatus whichdid not require a perforated inner tube but which replaced it by a cheapand easily available component which gave reduced pressure drop.

According to the present invention an apparatus for removingcontaminants from a liquid, which apparatus comprises a casing, dividedinto two compartments by a tubular fibrous filter, said fibrous filterbeing formed of fibres attached at each end to an end support, said endsupports being moveable axially relative to one another, and rotablerelative to one another about the longitudinal axis of the tubularfibrous filter, is characterised in that a helical spring is disposedwithin the tubular fibrous filter and is so dimensioned that it does notclose when the end supports are in their closest operational positionand resists inward movement of the fibres tending to close thecompartment surrounded by the tubular filter when the end supports aremoved axially towards each other and rotated to twist the fibre.

By using a helical spring in place of the perforated tube of the presentinvention adequate support can be given to the tubular fibrous filterboth during use and during backwashing to remove impurities. Helicalsprings are relatively easy to manufacture and were therefore cheaperthan using perforated tubes which will require more expensivefabrication techniques for their manufacture. The helical spring can beused to replace only the inner perforated tube disclosed in EP0 027 797.However it is preferred to eliminate the outer perforated tube also. Thefibres can be kept in compression by controlling the sequence ofrotation and axial movement instead. The radial force exerted by thehelical spring is sufficient to support the fibres as the bed of fibresforming the tubular filter contracts under the torsional stress appliedby relative rotation of the end supports.

The spring is so dimensioned that it does not close when the distancebetween the end supports is at its operational minimum, i.e. the turnsof the spring do not come into contact so preventing passage of liquidthrough the filter.

The ends of the spring can be free to rotate relative to the endsupports. However this will tend to produce wear of the end supportsunless the additional expense and complication of providing some kind ofbearing is incurred. It is therefore preferred to fix the spring to theend supports at both ends. It is an advantage of the present inventionthat the spring can accommodate the torsion resulting from the relativerotation of the end supports without giving any excessive increase inthe torque needed to give the required relative rotation of the endsupports.

The length of the spring can be such that it is in a neutral state(neither in compression or tension) when the end supports are at theirmaximum operational relative axial distance. It has been foundpreferable, however, for the length of the spring to be selected suchthat it is in the neutral state when the axial distance between the endsupports is at the minimum operational value.

The spacing of the turns of the spring is preferably such as to give themaximum open area between the turns so as to minimise pressure drop andto avoid high flow rate regions.

A specific embodiment of the invention will now be illustrated byreference to the accompanying figure which is a cross-section through anapparatus according to the invention.

The apparatus comprises a casing (1), having a vent (2) at its upperend. The vent (2) will normally be closed off by a pressure relief valveor a pressure gauge in use. The casing is divided into two compartmentsby a tubular fibrous filter, indicated generally at (3). The fibrousfilter comprise bundles of fibres secured at each end to end supports(5) and (6). End support (5) is fixed to the casing (1). End support (6)is attached to an actuating rod (7) by which can it can be moved axiallytowards end support (5) and also rotated relative to end support (5). Aliquid inlet (8) is provided in casing (1), opening into the outercompartment surrounding the tubular filter. A liquid outlet (9) isprovided in the base of the casing, opening into the compartment withinthe tubular filter.

A drain outlet (10) is provided through which the casing can be drainedif required. A helical spring (11) is disposed within the space withinthe tubular filter (3). One end (12) of the spring (11) is anchored inan opening in fixed end support (5). The other end (13) is anchored inmoveable end support (6).

In use the moveable end support (6) is moved from the position shown indotted lines in FIG. 1 to the position shown in full lines by retractionand rotation of the actuating rod. As a consequence the fibres move froma position in which they are parallel to the axis of the filter to onein which they are inclined to the axis. As a result the individualfibres are forced closer together so increasing their efficiency attrapping particles in the fluid or coalescing droplets of immisicibleliquid.

The movement of the actuating rod compresses the spring so that itcontinues to provide support over the whole length of the fibres withoutthe complex mechanical arrangement shown in EP 0 207 797.

When the tubular fibrous filter is rotated and compressed the springprovides radial support for the stressed fibres and allows the endplates to rotate and compress the tubular fibrous bed by acceptingtorsion and compression within the spring due to the low stiffness ofthe spring in the torsional and axial axes but high rigidity in theradial direction.

When it is desired to clean the filter the actuating rod (7) is extendedand rotated to return the moveable end support to the position shown indotted lines. This increases the spacing between the fibres sofacilitating backwashing.

I claim:
 1. An apparatus for removing contaminants from a liquid, whichapparatus comprises a casing, divided into two compartments by a tubularfibrous filter, said fibrous filter being formed of fibres attached ateach end to an end support, said end supports being moveable axiallyrelative to one another, and rotable relative to one another about thelongitudinal axis of the tubular fibrous filter, said apparatus furthercomprising a helical spring disposed within the tubular filter and is sodimensioned that it does not close when the end supports are in theirclosest operational position and resists inward movement of the fibrestending to close the compartment surrounded by the tubular filter whenthe end supports are moved axially towards each other and rotated totwist the fibre.
 2. The apparatus according to claim 1 in which thespring is fixed to the end supports at both of its ends.
 3. Theapparatus according to claim 1 wherein the length of the spring is suchthat it is in a neutral state when the axial distance between the endsupports is at a minimum operational value.
 4. The apparatus accordingto claim 2 wherein the length of the spring is such that it is in aneutral state when the axial distance between the end supports is at aminimum operational value.
 5. The apparatus of claim 1 wherein saidhelical spring is cylindrical.